Not at the ones I am familiar with. The New Carollton stop, or the Greenbelt stop are easiest. Not only does New carollton cost, It sells out. If you do 24 hrs in the NC park& ride, you may get ticketed.
Looks like Greenbelt allows 24 hr, but is not free.
http://www.wmata.com/metrorail/daily-parking.cfm
You can take the MARC from BWI to Union Station. A shuttle bus will take you from the terminal to the train stop.